Fuel delivery pipes are widely used in an electronic fuel injection system for a gasoline engine. There are two types; one is a return type having a return pipe in which fuel is delivered from a conduit having a fuel passage therein to fuel injectors via cylindrical sockets and then goes back to a fuel tank, and another is a non-return (return-less) type. Recently, for reducing vaporized gas caused by high temperature return fuel and for economical reasons, use of the non-return type is increasing and new problems are arising therefrom, those are, due to reflecting waves (shock waves) which are caused by reciprocal movements of valve operating spools for moving fuel injectors and due to fuel injection pressure pulsations, the fuel delivery pipes and their parts are vibrated thereby emitting uncomfortable noise.
Further, in those gasoline engines having a plurality of cylinders disposed in a V-shape or horizontal opposed shape and having a pair of right and left return-less type delivery pipes, injections are alternately done right and left, where at the moment of the valve opening or valve closing a kind of water hammer is produced. At a special engine rotation speed, a kind of standing wave is caused and a resonance is arised, pressure pulsations are increased, and further fuel injection instability and noise are increased. This phenomena are supposed to be a pulsation resonance in which a peculiar frequency of pressure pulsation wave becomes in coincident with a peculiar rotation speed of the engine, wherein the peculiar frequency are produced through overall overlapping process of the reflecting phenomena and passing phenomena caused in each boundary, such as a boundary between the delivery pipe and the fuel supply line.
In a so-called direct injection type engine in which fuel is directly injected into a combustion chamber, a high pressure supply pump is provided, and therefore a pulsation damper is provided so as to absorb the high pressure pulsations, whereby owing to its absorbing performance a resonance is not produced in general. However, in most cases having no pulsation damper, the resonance appears clearly, and the resonance point falls within the actual working rotation area of a gasoline engine. Accordingly, it is desired to eliminate the resonance.
FIG. 12 illustrates an ordinary automobile in which an automobile 11 (gasoline car) having an electronic fuel injection type V-shape engine 10 is provided with a supply line 13 from a fuel tank 12 to the engine 10, and the line 13 is supported on a front panel or beneath a floor panel by a few or ten or so many clips 14. Fuel supplied through the supply line 13 are transferred to the right and left connecting pipes 18, 19 by way of the branch connector 17, and then to the pair of right and left delivery pipes 15, 16 each of which supplies fuel to one side three cylinders. The pair of right and left delivery pipes 15, 16 mounted on the engine supply fuel to injectors but are non-return (return-less) type having no return circuit to a fuel tank.
As shown, in such an internal combustion engine of a V-shape or horizontal opposed shape utilizing a pair of right and left return-less type delivery pipes, due to the differences of elasticity or sectional flow area between delivery pipes and supply pipes or connecting pipes, as mentioned above, at a special engine rotation speed, a kind of standing wave is caused and a resonance is arised, reflection and passing of pressure pulsations in a boundary are increased, and further fuel injection instability and noise are increased, whereby a problem that uncomfortable noise is transmitted to a driver is arised.
Japanese Patent unexamined publication Hei 11-6438 190261 entitled “Delivery pipe” suggests a method for eliminating an engine stop due to fuel pressure pulsations during idling rotation taking the fuel pressure pulsations and resonance rotation into account.
Although the previously mentioned pulsation damper is utilized in direct injection type engines and some ordinary fuel injection (multi point injection: MPI) type engines, it is not easy to adopt the damper due to space requirements and economical reasons.
Japanese Patent unexamined publication No. 2000-329031 entitled “Fuel delivery pipe” suggests to provide a flexible absorbing surface on an outside wall of the conduit of the delivery pipe so as to suppress pressure pulsations.
Japanese Patent unexamined publication Sho 60-240867 entitled “Fuel supply conduit for fuel injection device of an internal combustion engine” relates to an improvement of a fuel delivery pipe wherein at least one wall of the fuel supply conduit is comprised of an elastic member for damping the fuel pulsations.
Similarly, in Japanese Patent unexamined publication Hei 8-326622 entitled “Fuel pressure pulsation damping device” and Japanese Patent unexamined publication Hei 11-37380 entitled “Delivery pipe”, improvements of fuel delivery pipe so as to suppress the pulsation are described.
It is an object of the invention to provide a pressure pulsation suppressing system of a fuel piping which is arranged to an MPI type gasoline engine having a plurality of cylinders disposed in a straight, V-shape or horizontal opposed shape with one or a pair of right and left return-less type delivery pipes each having no return circuit to a fuel tank.